U.S. patent number 8,120,836 [Application Number 12/719,702] was granted by the patent office on 2012-02-21 for luminance enhancement structure for reflective display devices.
This patent grant is currently assigned to SiPix Imaging, Inc.. Invention is credited to Craig Lin, Robert A. Sprague.
United States Patent |
8,120,836 |
Lin , et al. |
February 21, 2012 |
Luminance enhancement structure for reflective display devices
Abstract
The present invention is directed to luminance enhancement
structures for reflective display devices. The structure comprises
columns and grooves, wherein each of said grooves has a
cross-section comprising an apex angle and two edge lines. The
structure increases the overall reflectance by reducing the total
internal reflection, and as a result, the brightness of a display
device is increased.
Inventors: |
Lin; Craig (San Jose, CA),
Sprague; Robert A. (Saratoga, CA) |
Assignee: |
SiPix Imaging, Inc. (Fremont,
CA)
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Family
ID: |
42678043 |
Appl.
No.: |
12/719,702 |
Filed: |
March 8, 2010 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20100225999 A1 |
Sep 9, 2010 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61158636 |
Mar 9, 2009 |
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Current U.S.
Class: |
359/296; 345/33;
359/245; 349/139; 345/107; 359/316 |
Current CPC
Class: |
G02F
1/167 (20130101); G02F 1/133524 (20130101); G02F
1/1677 (20190101) |
Current International
Class: |
G02B
26/00 (20060101); G02F 1/03 (20060101); G02F
1/29 (20060101) |
Field of
Search: |
;359/296,245,253-254,265,290-291 ;349/33 ;345/107 ;430/31-32 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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WO 01/67170 |
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Sep 2001 |
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WO |
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WO 2008-122927 |
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Oct 2008 |
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WO |
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WO 2009/114361 |
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Sep 2009 |
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WO |
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Primary Examiner: Pinkney; Dawayne A
Attorney, Agent or Firm: Perkins Coie LLP
Parent Case Text
This application claims priority to U.S. Provisional Application
No. 61/158,636, filed Mar. 9, 2009; the content of which is
incorporated herein by reference in its entirety.
Claims
What is claimed is:
1. A display device assembly comprising a) a display panel which
comprises an array of display cells filled with a display fluid;
and b) a one-dimensional luminance enhancement structure comprising
columns and grooves, wherein each of said grooves has a
cross-section comprising an apex angle in the range of about
5-50.degree. and two edge lines, and said columns and grooves are
in an alternating order and in a continuous form in one direction,
wherein the luminance enhancement structure is on the viewing side
of the display device to allow incoming light from a light source
to transmit through the luminance enhancement structure and strike
the display panel and then to be reflected from the luminance
enhancement structure.
2. The assembly of claim 1, wherein said two edge lines are
straight lines and the apex angles of the grooves are not the same
throughout the structure.
3. The assembly of claim 2, wherein the two edge lines of the
cross-section are substantially equal for all grooves.
4. The assembly of claim 2, wherein the two edge lines are
substantially equal for some of the grooves and the two edge lines
are not equal for the remaining grooves.
5. The assembly of claim 2, wherein the two edge lines are not
equal for all grooves.
6. The assembly of claim 2, wherein the heights of the grooves are
substantially equal throughout the structure.
7. The assembly of claim 2, wherein the heights of the grooves
vary.
8. The assembly of claim 2, wherein the pitches of the grooves are
substantially equal for all grooves throughout the structure.
9. The assembly of claim 2, wherein the pitches of the grooves
vary.
10. The assembly of claim 1, wherein each of the two edge lines
comprise two or more segments of straight line and the different
segments of the straight line have different edge line angles.
11. The assembly of claim 10, wherein the apex angles of the
grooves are substantially equal for all grooves throughout the
structure.
12. The assembly of claim 10, wherein the edge lines appear
curved.
13. The assembly of claim 10, wherein the curved edge lines have
more than one curvature.
14. The assembly of claim 1, wherein the two edge lines of a single
groove have different numbers of segments of the straight line.
15. The assembly of claim 1, wherein said apex angle is in the
range of about 20.degree. to about 40.degree..
16. The assembly of claim 1, wherein the surface of the grooves is
not coated.
Description
FIELD OF THE INVENTION
The present invention is directed to a luminance enhancement
structure for reflective display devices.
BACKGROUND OF THE INVENTION
The lack of satisfactory brightness is often a concern for
electrophoretic display devices. Total internal reflection
inevitably would occur with electrophoretic display devices because
such a display device usually has components of a high refractive
index. Due to the component having a higher refractive index (e.g.,
about 1.5) than the air (which has a refractive index of about 1)
surrounding the display panel, some of the scattering light from
the display panel may reflect back to the display device by total
internal reflection. This total internal reflection phenomenon may
result in a loss of about 30-50% of the scattering light, thus
causing reduction in brightness of the display device.
SUMMARY OF THE INVENTION
The first aspect of the invention is directed to a luminance
enhancement structure which comprises columns and grooves, wherein
each of said grooves has a cross-section comprising an apex angle
and two edge lines.
In this aspect of the invention, the luminance enhancement
structure may have a one dimensional configuration or a two
dimensional configuration.
In one embodiment, the two edge lines are straight lines and the
apex angles of the grooves are not the same throughout the
structure. The two edge lines of the cross-section may be
substantially equal for all grooves, or the two edge lines may be
substantially equal for some of the grooves and the two edge lines
are not equal for the remaining grooves, or the two edge lines are
not equal for all grooves.
In the first aspect of the invention, the heights of the grooves
may be substantially equal throughout the structure or the heights
of the grooves may vary.
In the first aspect of the invention, the pitches of the grooves
may be substantially equal for all grooves throughout the structure
or the pitches of the grooves may vary.
In the first aspect of the invention, each of the two edge lines
may comprise two or more segments of straight line and the
different segments of the straight line have different edge line
angles. In this embodiment, the apex angles of the grooves are
substantially equal for all grooves throughout the structure. The
edge lines may appear curved. The curved edge lines may have more
than one curvature.
In one embodiment, the two edge lines of a single groove have
different numbers of segments of the straight line.
The apex angle may be in the range of about 5.degree. to about
50.degree., preferably in the range of about 20.degree. to about
40.degree..
In one embodiment, the surface of the grooves is not coated.
The second aspect of the invention is directed to a display device
assembly comprising a) a display panel which comprises an array of
display cells filled with a display fluid; and b) a luminance
enhancement structure on the viewing side of the display device,
wherein said luminance structure comprises columns and grooves,
wherein each of said grooves has a cross-section comprising an apex
angle and two edge lines.
In the assembly, the luminance enhancement structure may have a one
dimensional configuration or a two dimensional configuration.
In the assembly, the two edge lines are straight lines and the apex
angles of the grooves are not the same throughout the
structure.
In the assembly, each of the two edge lines may comprise two or
more segments of straight line and the different segments of the
straight line have different edge line angles. In this embodiment,
the apex angles of the grooves are substantially equal for all
grooves throughout the structure.
In the assembly, the edge lines may appear curved. In this
embodiment, the curved edge lines may have more than one
curvature.
In the assembly, the two edge lines of a single groove may have
different numbers of segments of the straight line.
In the assembly, the apex angle is in the range of about 5.degree.
to about 50.degree., preferably in the range of about 20.degree. to
about 40.degree..
In the assembly, the surface of the grooves is not coated.
The assembly may further comprise a common electrode layer and a
backplane.
The luminance enhancement structure increases the overall
reflectance by reducing the total internal reflection. As a result,
the brightness of a display device is increased. Furthermore, the
structure can be fabricated by a cost effective roll-to-roll
manufacturing process.
BRIEF DISCUSSION OF THE DRAWINGS
FIG. 1 depicts a cross-section view of a display device.
FIG. 2a is a cross-section view of a luminance enhancement
structure of the present invention.
FIGS. 2b and 2c are a three-dimensional view of the luminance
enhancement structure.
FIG. 3a depicts a luminance enhancement structure having apex
angles of substantially the same size.
FIG. 3b depicts the first aspect of the present invention.
FIG. 3c-3i depict the second aspect of the present invention.
FIG. 4 is a cross-section view of a luminance enhancement structure
of the present invention on the viewing side of a display
device.
FIG. 5 depicts an embodiment of the present invention which
comprises a display device and a luminance enhancement structure on
the viewing side of the display device.
FIGS. 6a-6b illustrate the dimensions of a luminance enhancement
structure.
FIGS. 7a-7g show an example of how the luminance enhancement
structure is fabricated.
DETAILED DESCRIPTION OF THE INVENTION
I. Definitions
The technical term "total internal reflection" used in this
application refers to an optical phenomenon that occurs when a ray
of light strikes a medium boundary at an angle larger than the
critical angle (defined below) with respect to the normal axis to
the surface. This can only occur where light travels from a medium
with a higher refractive index to one with a lower refractive
index.
Generally speaking, when a ray of light crosses a boundary between
materials with different refractive indices, the light will be
partially refracted at the boundary surface, and partially
reflected. However, if the angle of incidence is greater than the
critical angle, the light will stop crossing the boundary and
instead be totally reflected back.
The critical angle is calculated based on the equation of Snell's
law: C=sin.sup.-1(n2/n1) wherein n1 and n2 are the refractive
indices of the two different media, with n1 being the higher
refractive index and n2 being the lower refractive index.
II. Display Devices
FIG. 1 illustrates a display device (100). The device comprises an
array of display cells (101) which are filled with a display fluid
(102) and sandwiched between two electrode layers (104 and 105).
Each of the display cells is surrounded by partition walls
(103).
For an electrophoretic display, the display cells are filled with
an electrophoretic fluid which comprises charged pigment particles
dispersed in a solvent. The display fluid may be a system
comprising one or two types of particles.
In the system comprising only one type of particles, the charged
pigment particles are dispersed in a solvent of a contrasting
color. The charged particles will be drawn to one of the electrode
layers (104 or 105), depending on the potential difference of the
two electrode layers, thus causing the display panel to show either
the color of the particles or the color of the solvent, on the
viewing side.
In a system comprising particles carrying opposite charges and of
two contrasting colors, the particles would move to one electrode
layer or the other, based on the charge that they carry and the
potential difference of the two electrode layers, causing the
display panel to show the two contrasting colors, on the viewing
side. In this case, the particles may be dispersed in a clear
solvent.
The display cells may also be filled with a liquid crystal
composition. In addition, it is understood that the present
invention is applicable to all types of reflective display
devices.
For a segment display device, the two electrode layers (104 and
105) are one common electrode (e.g., ITO) and one patterned segment
electrode layer, respectively. For an active matrix display device,
the two electrode layers (104 and 105) are one common electrode and
an array of thin film transistor pixel electrodes, respectively.
For a passive matrix display device, the two electrode layers (104
and 105) are two line-patterned electrode layers.
The patterned segment electrode layer (in a segment display device)
or the thin film transistor pixel electrodes (in an active matrix
display device) may be referred to as a "backplane", which along
with the common electrode drives the display device.
The electrode layers are usually formed on a substrate layer (106)
[(such as polyethylene terephthalate (PET)). The substrate layer
may also be a glass layer.
For a microcup-based display device disclosed in U.S. Pat. No.
6,930,818, the content of which is incorporated herein by reference
in its entirety, the filled display cells are sealed with a
polymeric sealing layer. Such a display device may be viewed from
the sealing layer side or the side opposite the sealing layer side,
depending on the transparency of the materials used and the
application.
III. The Luminance Enhancement Structure
FIG. 2a is a cross-section view of the luminance enhancement
structure (200) of the present invention in general. There are
multiple columns (202) and grooves (203) across the structure. The
cross-section (201) of the grooves (203) has a top point A and a
base line (b). The dotted lines connecting the top point A to the
two ends (E1 and E2) of the base line are referred to as "edge
lines". The dotted line means that the edge line may be a straight
line or may comprise two or more segments of straight line.
The two edge lines in a groove form an apex angle .alpha.. The
surface (204) of the grooves (203) is optically flat or may be
coated with a metal layer.
In the context of this application, the terms "groove" or "grooves"
refers to the groove or grooves the surface of which is either
uncoated or coated. In one embodiment of the present invention, the
surface of the groove or grooves is preferably uncoated.
The columns (202) have a top surface (205). The thickness ("t") of
the luminance enhancement structure may be in the range of about 10
.mu.m to about 200 .mu.m.
The luminance enhancement structure is formed from a material
having a refractive index of about 1.4 to 1.7. The luminance
enhancement structure is transparent.
The fabrication of such a luminance enhancement structure is
illustrated in a section below.
FIG. 2b is a three-dimensional view of the luminance enhancement
structure (200) in a one-dimensional configuration (i.e., the
columns and grooves are in alternating order and are in continuous
form in one direction). FIG. 2c is a three-dimensional view of the
luminance enhancement structure (200) in a two dimensional
configuration.
FIG. 3a shows a luminance enhancement structure wherein the grooves
have two edge lines which are straight lines and the apex angles
(.alpha.) are substantially equal for all grooves throughout the
structure.
In one embodiment, the two edge lines of the cross-section are
substantially equal (i.e., isosceles triangular cross-section) for
all grooves. In another embodiment, the two edge lines are
substantially equal for some of the grooves and the two edge lines
are not equal for the remaining grooves. In a further embodiment,
the two edge lines are different for all grooves.
In one embodiment, the heights "h" of the grooves are substantially
equal throughout the structure. In another embodiment, the heights
of the grooves vary.
In one embodiment, the pitches ("p") of the grooves are
substantially equal for all grooves throughout the structure. In
another embodiment, the pitches "p" of the grooves vary. The term
"pitch" is defined as the distance between one end point (E1) of
the base line (b) of one groove and the corresponding point (E1')
of the next groove. In other words, the term "pitch" is the sum of
the width of the base line (b) and the width of the top surface of
a column between the two grooves.
In the first aspect of the invention as shown in FIG. 3b, the two
edge lines are straight lines and the apex angles .alpha., however,
are not all equal for the grooves. For example, there may be 70% of
the apex angles are substantially equal while the remaining apex
angles vary.
In one embodiment of the first aspect of the invention, the two
edge lines of the cross-section are substantially equal (i.e.,
isosceles triangular cross-section) for all grooves. In another
embodiment, the two edge lines are substantially equal for some of
the grooves and the two edge lines are not equal for the remaining
grooves. In a further embodiment, the two edge lines are different
for all grooves.
In one embodiment, the apex angles have no more than five different
sizes throughout the structure.
In one embodiment of the first aspect of the invention, the heights
"h" of the grooves are substantially equal throughout the
structure. In another embodiment, the heights of the grooves
vary.
In one embodiment of the first aspect of the invention, the pitches
("p") of the grooves are substantially equal for all grooves
throughout the structure. In another embodiment, the pitches ("p")
of the grooves vary.
In any case, the grooves of different apex angles are randomly
located in the luminance enhancement structure.
The luminance enhancement resulted from different apex angles as
described as the first aspect of the invention may be similarly
achieved by maintaining the apex angles substantially equal while
varying the angles of the edge lines of the grooves. This
constitutes the second aspect of the present invention as shown in
FIGS. 3c-3i. In this aspect of the invention, the edge lines of the
cross section (301) may comprise two or more segments of straight
line and the different segments of the straight line have different
edge line angles (expressed as ELA in the drawings). The term "edge
line angle" is referred to the angle of a segment of the straight
line from the normal axis.
In this type of design, the apex angles may be maintained
substantially equal for all grooves throughout the structure. In
one embodiment, the apex angles may vary; however, it is not
needed.
In FIG. 3c, each edge line is formed of two segments of straight
line whereby ELA1 is not equal to ELA2 and ELA3 is not equal to
ELA4. In FIG. 3d, each edge line is formed of four segments of the
straight line and the edge line angles of the four segments of the
straight line are all different.
It is noted that while the number of the segments increases, the
edge lines would appear to be curved as shown in FIG. 3e. It is
also understood that the curved line may consist of more than one
curvature (see FIG. 3f), depending on how the segments of the
straight line are connected.
In FIG. 3g, ELA2 is greater than ELA1. In FIG. 3h, ELA1 is greater
than ELA2.
In one embodiment of the second aspect of the invention, the two
edge lines of a single groove may have different numbers of
segments of straight line. For example, as shown in FIG. 3i, one of
the edge lines of a groove is formed of two segments of straight
line while the other edge line is formed of three segments of
straight line.
In one embodiment, all grooves have the same set of two edge
lines.
Regardless of the configurations, the size of the apex angles
throughout this application, is preferably within a certain range
in order for the luminance enhancement structure to be effective,
which is illustrated below.
In addition, in both the first and second aspects of the invention,
the luminance enhancement structure may be one dimensional (FIG.
2b) or two dimensional (FIG. 2c). However, it is preferable that
the structure is one dimensional.
Unless otherwise stated, the term "substantially equal" or
"substantially the same" is intended to refer to the fact that the
variances for the angles or distances are within the range of
manufacturing tolerances.
IV. Display Device with the Luminance Enhancement Structure
FIG. 4 depicts a cross-section view of the luminance enhancement
structure on the viewing side of the display device. As shown, the
luminance enhancement structure of FIG. 2a has been turned
180.degree., with the top surface (205) of the columns (202) now in
optical contact with the top substrate layer (106T) of the display
device, which means that there is no air gap between the top
surface 205 and the substrate layer 106T. This may be achieved by
an adhesive material, such as the Norland.RTM. optical
adhesive.
The space within the grooves (203) usually is filled with air. It
is also possible for the space to be in a vacuum state.
Alternatively, the space in the grooves (203) may be filled with a
low refractive index material, lower than the refractive index of
the material forming the luminance enhancement structure.
The thickness of the top substrate layer (106T) is usually between
about 5 .mu.m to about 175 .mu.m, more preferably between about 1
.mu.m to about 50 .mu.m. In order to achieve the effect of the
luminance enhancement structure, the top substrate layer is
preferably as thin as possible (e.g., about 1 .mu.m to about
25.mu.). During formation of a display cell layer on the substrate
layer, preferably the substrate layer is adhered to a base layer
for mechanical strength and the display cells are formed on the
side of the substrate layer. After the display cells are formed,
the base layer is removed and a luminance enhancement structure is
laminated (optionally with an adhesive layer) to the substrate
layer to complete the assembly.
FIG. 5 shows an embodiment of the assembly comprising a display
device and a luminance enhancement structure (501) on the viewing
side of the display device comprising display cells (504). In this
embodiment, the ratio of the width (d.sub.1) of the top surface of
the columns (503) to the distance (d.sub.2) between the luminance
enhancement structure (501) and the top (502) of the display fluid
is at least about 2. It is noted that the distance d.sub.2 may
comprise an electrode layer (505), the substrate layer (506) and
optionally an adhesive layer (507).
V. Dimensions of the Luminance Enhancement Structure
FIGS. 6a-6b illustrate the dimensions of a luminance enhancement
structure of the present invention and show how the luminance
enhancement structure may enhancement brightness.
In FIG. 6a, it is shown that the design aims to ensure an angle of
incidence .theta..sub.1 to be smaller than the critical angle
C.sub.1 (not shown) at the boundary between the top surface (607)
of the luminance enhancement structure (600) and air.
The critical angle C.sub.1, in this case, is about 42.degree. based
on the refractive index of the material for the luminance
enhancement structure being 1.5 and the refractive index of air
surrounding the top surface of the luminance enhancement structure
being 1.
As shown in FIG. 6a, the light (602) scattered from the pigment
particles through the top surface (606) of the display device is
reflected at the tilted surface (603) of the groove (601) and
reaches the top surface (607) of the luminance enhancement
structure (600). In order for the angle of incidence
(.theta..sub.1) at the top surface of the luminance enhancement
structure to be smaller than 42.degree., the top angle .alpha. of
the groove (601) is preferably in the range of 5 to 50.degree.,
more preferably in the range of from about 20.degree. to about
40.degree.. As a result, the angle of incidence .theta..sub.1 will
be smaller than the angle .gamma., which reduces the chance of
total internal reflection at the top surface and increases the
overall optical efficiency. The angle .gamma. is an angle at the
intersection of the light (602) and the normal axis (marked Y) of
the surface (606) of the display device.
An incoming light (not shown) from a light source transmits through
the luminance enhancement structure and strikes the display device
and is then reflected with a scattering profile. The scattered
light 602 in FIG. 6a is a typical example of such a reflected
light.
FIG. 6b demonstrates that the tilted surface (603) of the groove
(601) will reflect incoming light by total internal reflection. The
design aims to ensure that the light striking the tilted surface
(603) of the groove (601) will be reflected instead of transmitting
through the space within the groove. The critical angle C.sub.2
(not shown) at the boundary between the tilted surface (603) and
the space within the groove may be calculated based on the
refractive index of the material for the luminance enhancement
structure and the refractive index of what is filled in the space
of the groove (601). If the groove is unfilled, the refractive
index of air is about 1. With the refractive index of the material
for the luminance enhancement structure being about 1.5, the
critical angle C.sub.2 would be about 42.degree.. When the angle of
incidence .theta..sub.2 of the light (608) coming from the surface
(607) is greater than 42.degree., the light striking the tilted
surface (603) will be totally internal reflected towards the
boundary 606 which is desired in this case because otherwise, the
light would transmit through the space in the groove.
A reflective tilted surface may be achieved by coating a metal
layer over the surface of the groove. However, in one embodiment of
the present invention, the surface of the grooves is preferably
uncoated.
Since the light striking the tilted surface will be reflected as
discussed above, the off-axis light may move toward the on-axis
direction. In other words, the display device with a luminance
enhancement structure of the present invention will be brighter at
the on-axis angles by both reducing total internal reflection and
utilizing the off-axis light.
However, the luminance enhancement structure is also sensitive to
the direction of the light sources. The more light that comes from
a greater angle of incidence, the worse the enhancement performance
is. Furthermore, the luminance enhancement performance is at the
maximum when all of the light sources are at an angle of incidence
of 0.degree..
Although in most cases the direction of light sources cannot be
controlled for a display device, generally any light sources coming
from above the display device (such as from a ceiling) would
provide the desired luminance conditions.
VI. Fabrication of the Luminance Enhancement Structure
The luminance enhancement structure may be fabricated in many
different ways.
In one embodiment, the luminance enhancement structure may be
fabricated separately and then laminated over the viewing side of
the display device. For example, the luminance enhancement
structure may be fabricated by embossing as shown in FIG. 7a. The
embossing process is carried out at a temperature higher than the
glass transition temperature of the embossable composition (700)
coated on a substrate layer (701). The embossing is usually
accomplished by a mold which may be in the form of a roller, plate
or belt. The embossable composition may comprise a thermoplastic,
thermoset or a precursor thereof. More specifically, the embossable
composition may comprise multifunctional acrylate or methacrylate,
multifunctional vinylether, multifunctional epoxide or an oligomer
or polymer thereof. The glass transition temperatures (or Tg) for
this class of materials usually range from about -70.degree. C. to
about 150.degree. C., preferably from about -20.degree. C. to about
50.degree. C. The embossing process is typically carried out at a
temperature higher than the Tg. A heated mold or a heated housing
substrate against which the mold presses may be used to control the
embossing temperature and pressure. The mold is usually formed of a
metal such as nickel. The hardening of the embossable composition
may be accomplished by cooling, solvent evaporation, cross-linking
by radiation, heat or moisture.
The mold is preferably manufactured by the diamond turning
technique. Typically the mold is made by diamond turning technique
on a cylindrical blank known as a roll. The surface of the roll is
typically of hard copper, although other materials may be used. The
pattern on the mold (roll) is the opposite of the intended
luminance enhancement structure. In other words, the roll will show
sharp protruding patterns which are corresponding to the grooves of
the luminance enhancement structure. The pattern on the roll is
formed in a continuous manner around the circumference of the roll.
In a preferred embodiment, the indentations on the surface of the
roll are produced by a technique known as thread cutting. In thread
cutting, a single, continuous indentation is cut on the roll while
the diamond cutter is moved in a direction transverse to the
turning roll. If the mold to be produced has a constant pitch,
during manufacture of the mold, the roll will move at a constant
velocity. A typical diamond turning machine will provide
independent control of the depth that the cutter penetrates the
roll, the horizontal and vertical angles that the cutter makes to
the roll and the transverse velocity of the cutter.
As shown in FIG. 7a, the mold creates the grooves (703) and is
released during or after the embossable composition is
hardened.
The hardening of the embossable composition may be accomplished by
cooling, solvent evaporation, cross-linking by radiation, heat or
moisture.
The refraction index of the material for forming the luminance
enhancement structure is preferably greater than about 1.4, more
preferably between about 1.5 and about 1.7.
The luminance enhancement structure may be used as is or further
coated with a metal layer.
The metal layer (707) is then deposited over the surface (706) of
the grooves (703) as shown in FIG. 7b. Suitable metals for this
step may include, but are not limited to, aluminum, copper, zinc,
tin, molybdenum, nickel, chromium, silver, gold, iron, indium,
thallium, titanium, tantalum, tungsten, rhodium, palladium,
platinum and cobalt. Aluminum is usually preferred. The metal
material must be reflective, and it may be deposited on the surface
(706) of the grooves, using a variety of techniques such as
sputtering, evaporation, roll transfer coating, electroless plating
or the like.
In order to facilitate formation of the metal layer only on the
intended surface (i.e., the surface 706 of the grooves), a
strippable masking layer may be coated before metal deposition,
over the surface on which the metal layer is not to be deposited.
As shown in FIG. 7c, a strippable masking layer (704) is coated
onto the surface (705) between the openings of the grooves. The
strippable masking layer is not coated on the surface (706) of the
grooves.
The coating of the strippable masking layer may be accomplished by
a printing technique, such as flexographic printing, driographic
printing, electrophotographic printing, lithographic printing,
gravure printing, thermal printing, inkjet printing or screen
printing. The coating may also be accomplished by a
transfer-coating technique involving the use of a release layer.
The strippable masking layer preferably has a thickness in the
range of about 0.01 to about 20 microns, more preferably about 1 to
about 10 microns.
For ease of stripping, the layer is preferably formed from a
water-soluble or water-dispersible material. Organic materials may
also be used. For example, the strippable masking layer may be
formed from a re-dispersible particulate material. The advantage of
the re-dispersible particulate material is that the coated layer
may be easily removed without using a solubility enhancer. The term
"re-dispersible particulate" is derived from the observation that
the presence of particles in the material in a significant quantity
will not decrease the stripping ability of a dried coating and, on
the contrary, their presence actually enhances the stripping speed
of the coated layer.
The re-dispersible particulate consists of particles that are
surface treated to be hydrophilic through anionic, cationic or
non-ionic functionalities. Their sizes are in microns, preferably
in the range of about 0.1 to about 15 um and more preferably in the
range of about 0.3 to about 8 um. Particles in these size ranges
have been found to create proper surface roughness on a coated
layer having a thickness of <15 um. The re-dispersible
particulate may have a surface area in the range of about 50 to
about 500 m.sup.2/g, preferably in the range of about 200 to about
400 m.sup.2/g. The interior of the re-dispersible particulate may
also be modified to have a pore volume in the range of about 0.3 to
about 3.0 ml/g, preferably in the range of about 0.7 to about 2.0
ml/g.
Commercially available re-dispersible particulates may include, but
are not limited to, micronized silica particles, such as those of
the Sylojet series or Syloid series from Grace Davison, Columbia,
Md., USA.
Non-porous nano sized water re-dispersible colloid silica
particles, such as LUDOX AM can also be used together with the
micron sized particles to enhance both the surface hardness and
stripping rate of the coated layer.
Other organic and inorganic particles, with sufficient
hydrophilicity through surface treatment, may also be suitable. The
surface modification can be achieved by inorganic and organic
surface modification. The surface treatment provides the
dispensability of the particles in water and the re-wettability in
the coated layer.
In FIG. 7d, a metal layer (707) is shown to be deposited over the
entire surface, including the surface (706) of the grooves and the
surface (705) between the grooves. Suitable metal materials are
those as described above. The metal material must be reflective and
may be deposited by a variety of techniques previously
described.
FIG. 7e shows the structure after removal of the strippable masking
layer (704) with the metal layer (707) coated thereon. This step
may be carried out with an aqueous or non-aqueous solvent such as
water, MEK, acetone, ethanol or isopropanol or the like, depending
on the material used for the strippable masking layer. The
strippable masking layer may also be removed by mechanical means,
such as brushing, using a spray nozzle or peeling it off with an
adhesive layer. While removing the strippable masking layer (704),
the metal layer (707) deposited on the strippable masking layer is
also removed, leaving the metal layer (707) only on the surface
(706) of the grooves.
FIGS. 7f and 7g depict an alternative process for depositing the
metal layer. In FIG. 7f, a metal layer (707) is deposited over the
entire surface first, including both the surface (706) of the
grooves and the surface (705) between the grooves. FIG. 7g shows
that the film of grooves deposited with a metal layer (707) is
laminated with a film (717) coated with an adhesive layer (716).
The metal layer (707) on top of the surface (705) may be
conveniently peeled off when the film of grooves is delaminated
(separated) from the adhesive layer (716) coated film (717). The
thickness of the adhesive layer (716) on the adhesive coated film
is preferably in the range of about 1 to about 50 um and more
preferably in the range of about 2 to about 10 um.
The luminance enhancement structure comprising grooves (uncoated or
coated with a metal layer) is then laminated over a layer of
display cells as described above.
For a two dimensional luminance enhancement structure, it may be
manufactured by a self-aligned process as disclosed in U.S.
application Ser. No. 12/323,300, filed Nov. 25, 2008, the content
of which is incorporated herein by reference in its entirety. In
the self-aligned process, the display cells are formed by a
photolithography process, utilizing the luminance enhancement
structure as a photomask.
While the present invention has been described with reference to
the specific embodiments thereof, it should be understood by those
skilled in the art that various changes may be made and equivalents
may be substituted without departing from the true spirit and scope
of the invention. In addition, many modifications may be made to
adapt a particular situation, materials, compositions, processes,
process step or steps, to the objective, spirit and scope of the
present invention. All such modifications are intended to be within
the scope of the claims appended hereto.
* * * * *